openssl學習之ccm，gcm 模式

阿新 • • 發佈：2019-01-19

openssl中添加了對AES ccm 和gcm模式的支援。下面的內容主要是對這兩個模式相關資料的收集以及整理。

一，CCM

CCM （counter with CBC-MAC)定義在分組長度為128位的加密演算法中，如，AES 的分組長度為128。組成AES-CCM演算法的關鍵組成是CTR工作模式以及CMAC認證演算法。Wifi 的WPE協議中使用了AES-CCM。在HMAC中我們介紹CCM是屬於一種E&M（認證並且加密），首先我們來看一下AES-CCM模式的輸入輸出。

首先介紹兩個引數設定：

L：長度域，取值為2~8 ，openssl中預設的為8。

M：tag的長度，合法的值為：4,6,8,10,12,14 和16。openssl中預設的為12

key	16,24,32
None	15-L
Message to authenticate and encrypt	len(Msg)
Additional authenticated data	len(AAD)

其中對訊息長度有：0<= len(Msg)<= 2^(8L);

對附加資料長度有：0<= len(AAD)< 2^64;

/* Simple AES CCM test program, uses the same NIST data used for the FIPS
 * self test but uses the application level EVP APIs.
 */
#include <stdio.h>
#include <openssl/bio.h>
#include <openssl/evp.h>

/* AES-CCM test data from NIST public test vectors */

static const unsigned char ccm_key[] = {
	0xce,0xb0,0x09,0xae,0xa4,0x45,0x44,0x51,0xfe,0xad,0xf0,0xe6,
	0xb3,0x6f,0x45,0x55,0x5d,0xd0,0x47,0x23,0xba,0xa4,0x48,0xe8
};
// 隨機數，每次加密針對相同的KEY使用不同的NONCE。否則會破壞CCM模式的安全性（RFC3610）
static const unsigned char ccm_nonce[] = {
	0x76,0x40,0x43,0xc4,0x94,0x60,0xb7
};
//附加資料
static const unsigned char ccm_adata[] = {
	0x6e,0x80,0xdd,0x7f,0x1b,0xad,0xf3,0xa1,0xc9,0xab,0x25,0xc7,
	0x5f,0x10,0xbd,0xe7,0x8c,0x23,0xfa,0x0e,0xb8,0xf9,0xaa,0xa5,
	0x3a,0xde,0xfb,0xf4,0xcb,0xf7,0x8f,0xe4
};
//plaintext 表示明文
static const unsigned char ccm_pt[] = {
	0xc8,0xd2,0x75,0xf9,0x19,0xe1,0x7d,0x7f,0xe6,0x9c,0x2a,0x1f,
	0x58,0x93,0x9d,0xfe,0x4d,0x40,0x37,0x91,0xb5,0xdf,0x13,0x10
};
//ciphertext 表示密文
static const unsigned char ccm_ct[] = {
	0x8a,0x0f,0x3d,0x82,0x29,0xe4,0x8e,0x74,0x87,0xfd,0x95,0xa2,
	0x8a,0xd3,0x92,0xc8,0x0b,0x36,0x81,0xd4,0xfb,0xc7,0xbb,0xfd
};
//tag 表示tag資料
static const unsigned char ccm_tag[] = {
	0x2d,0xd6,0xef,0x1c,0x45,0xd4,0xcc,0xb7,0x23,0xdc,0x07,0x44,
	0x14,0xdb,0x50,0x6d
};

void aes_ccm_encrypt(void)
{
	EVP_CIPHER_CTX *ctx;
	int outlen, tmplen;
	unsigned char outbuf[1024];
	printf("AES CCM Encrypt:\n");
	printf("Plaintext:\n");
	BIO_dump_fp(stdout, ccm_pt, sizeof(ccm_pt));
	ctx = EVP_CIPHER_CTX_new();
	/* Set cipher type and mode */
	EVP_EncryptInit_ex(ctx, EVP_aes_192_ccm(), NULL, NULL, NULL);
	/* Set nonce length if default 96 bits is not appropriate */
	EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_IVLEN, sizeof(ccm_nonce), NULL);
	/* Set tag length */
	EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_TAG, sizeof(ccm_tag), NULL);
	/* Initialise key and IV */
	EVP_EncryptInit_ex(ctx, NULL, NULL, ccm_key, ccm_nonce);
	/* Set plaintext length: only needed if AAD is used*/
        //輸入輸出需設定為NULL
	EVP_EncryptUpdate(ctx, NULL, &outlen, NULL, sizeof(ccm_pt));
	/* Zero or one call to specify any AAD */
        //設定AAD，out引數需設定為NULL
	EVP_EncryptUpdate(ctx, NULL, &outlen, ccm_adata, sizeof(ccm_adata));
	/* Encrypt plaintext: can only be called once */
	EVP_EncryptUpdate(ctx, outbuf, &outlen, ccm_pt, sizeof(ccm_pt));
	/* Output encrypted block */
	printf("Ciphertext:\n");
	BIO_dump_fp(stdout, outbuf, outlen);
	/* Finalise: note get no output for CCM */
	EVP_EncryptFinal_ex(ctx, outbuf, &outlen);
	/* Get tag */
	EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_GET_TAG, 16, outbuf);
	/* Output tag */
	printf("Tag:\n");
	BIO_dump_fp(stdout, outbuf, 16);
	EVP_CIPHER_CTX_free(ctx);
}

void aes_ccm_decrypt(void)
{
	EVP_CIPHER_CTX *ctx;
	int outlen, tmplen, rv;
	unsigned char outbuf[1024];
	printf("AES CCM Derypt:\n");
	printf("Ciphertext:\n");
	BIO_dump_fp(stdout, ccm_ct, sizeof(ccm_ct));
	ctx = EVP_CIPHER_CTX_new();
	/* Select cipher */
	EVP_DecryptInit_ex(ctx, EVP_aes_192_ccm(), NULL, NULL, NULL);
	/* Set nonce length, omit for 96 bits */
	EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_IVLEN, sizeof(ccm_nonce), NULL);
	/* Set expected tag value */
	EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_TAG,
					sizeof(ccm_tag), (void *)ccm_tag);
	/* Specify key and IV */
	EVP_DecryptInit_ex(ctx, NULL, NULL, ccm_key, ccm_nonce);
	/* Set ciphertext length: only needed if we have AAD */
	EVP_DecryptUpdate(ctx, NULL, &outlen, NULL, sizeof(ccm_ct));
	/* Zero or one call to specify any AAD */
	EVP_DecryptUpdate(ctx, NULL, &outlen, ccm_adata, sizeof(ccm_adata));
	/* Decrypt plaintext, verify tag: can only be called once */
	rv = EVP_DecryptUpdate(ctx, outbuf, &outlen, ccm_ct, sizeof(ccm_ct));
	/* Output decrypted block: if tag verify failed we get nothing */
	if (rv > 0)
	{
		printf("Plaintext:\n");
		BIO_dump_fp(stdout, outbuf, outlen);
	}
	else
		printf("Plaintext not available: tag verify failed.\n");
	EVP_CIPHER_CTX_free(ctx);
}

int main(int argc, char **argv)
{
	aes_ccm_encrypt();
	aes_ccm_decrypt();
}

2，GCM

GCM基於並行化設計，因此可以提供高效的吞吐率和低成本、低時延。本質是訊息在變形的CTR模式下加密，密文結果與金鑰以及訊息長度在GF（2^128）域上相乘，計算流程如下所示。其輸入輸出和CCM基本一致。CCM和GCM的具體計算過程可以參看《密碼學與網路安全》第五版，書中有詳細的介紹。FRC5288 中介紹了TLS1.2 中的GCM應用。下面貼出openssl中AES-GCM的例項。

/* Simple AES GCM test program, uses the same NIST data used for the FIPS
 * self test but uses the application level EVP APIs.
 */
#include <stdio.h>
#include <openssl/bio.h>
#include <openssl/evp.h>

/* AES-GCM test data from NIST public test vectors */

static const unsigned char gcm_key[] = {
        0xee,0xbc,0x1f,0x57,0x48,0x7f,0x51,0x92,0x1c,0x04,0x65,0x66,
        0x5f,0x8a,0xe6,0xd1,0x65,0x8b,0xb2,0x6d,0xe6,0xf8,0xa0,0x69,
        0xa3,0x52,0x02,0x93,0xa5,0x72,0x07,0x8f
};

static const unsigned char gcm_iv[] = {
        0x99,0xaa,0x3e,0x68,0xed,0x81,0x73,0xa0,0xee,0xd0,0x66,0x84
};

static const unsigned char gcm_pt[] = {
        0xf5,0x6e,0x87,0x05,0x5b,0xc3,0x2d,0x0e,0xeb,0x31,0xb2,0xea,
        0xcc,0x2b,0xf2,0xa5
};

static const unsigned char gcm_aad[] = {
        0x4d,0x23,0xc3,0xce,0xc3,0x34,0xb4,0x9b,0xdb,0x37,0x0c,0x43,
        0x7f,0xec,0x78,0xde
};

static const unsigned char gcm_ct[] = {
        0xf7,0x26,0x44,0x13,0xa8,0x4c,0x0e,0x7c,0xd5,0x36,0x86,0x7e,
        0xb9,0xf2,0x17,0x36
};

static const unsigned char gcm_tag[] = {
        0x67,0xba,0x05,0x10,0x26,0x2a,0xe4,0x87,0xd7,0x37,0xee,0x62,
        0x98,0xf7,0x7e,0x0c
};

void aes_gcm_encrypt(void)
{
        EVP_CIPHER_CTX *ctx;
        int outlen, tmplen;
        unsigned char outbuf[1024];
        printf("AES GCM Encrypt:\n");
        printf("Plaintext:\n");
        BIO_dump_fp(stdout, gcm_pt, sizeof(gcm_pt));
        ctx = EVP_CIPHER_CTX_new();
        /* Set cipher type and mode */
        EVP_EncryptInit_ex(ctx, EVP_aes_256_gcm(), NULL, NULL, NULL);
        /* Set IV length if default 96 bits is not appropriate */
        EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, sizeof(gcm_iv), NULL);
        /* Initialise key and IV */
        EVP_EncryptInit_ex(ctx, NULL, NULL, gcm_key, gcm_iv);
        /* Zero or more calls to specify any AAD */
        EVP_EncryptUpdate(ctx, NULL, &outlen, gcm_aad, sizeof(gcm_aad));
        /* Encrypt plaintext */
        EVP_EncryptUpdate(ctx, outbuf, &outlen, gcm_pt, sizeof(gcm_pt));
        /* Output encrypted block */
        printf("Ciphertext:\n");
        BIO_dump_fp(stdout, outbuf, outlen);
        /* Finalise: note get no output for GCM */
        EVP_EncryptFinal_ex(ctx, outbuf, &outlen);
        /* Get tag */
        EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, 16, outbuf);
        /* Output tag */
        printf("Tag:\n");
        BIO_dump_fp(stdout, outbuf, 16);
        EVP_CIPHER_CTX_free(ctx);
}

void aes_gcm_decrypt(void)
{
        EVP_CIPHER_CTX *ctx;
        int outlen, tmplen, rv;
        unsigned char outbuf[1024];
        printf("AES GCM Derypt:\n");
        printf("Ciphertext:\n");
        BIO_dump_fp(stdout, gcm_ct, sizeof(gcm_ct));
        ctx = EVP_CIPHER_CTX_new();
        /* Select cipher */
        EVP_DecryptInit_ex(ctx, EVP_aes_256_gcm(), NULL, NULL, NULL);
        /* Set IV length, omit for 96 bits */
        EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, sizeof(gcm_iv), NULL);
        /* Specify key and IV */
        EVP_DecryptInit_ex(ctx, NULL, NULL, gcm_key, gcm_iv);
#if 0
        /* Set expected tag value. A restriction in OpenSSL 1.0.1c and earlier
         * required the tag before any AAD or ciphertext */
        EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, sizeof(gcm_tag), gcm_tag);
#endif
        /* Zero or more calls to specify any AAD */
        EVP_DecryptUpdate(ctx, NULL, &outlen, gcm_aad, sizeof(gcm_aad));
        /* Decrypt plaintext */
        EVP_DecryptUpdate(ctx, outbuf, &outlen, gcm_ct, sizeof(gcm_ct));
        /* Output decrypted block */
        printf("Plaintext:\n");
        BIO_dump_fp(stdout, outbuf, outlen);
        /* Set expected tag value. Works in OpenSSL 1.0.1d and later */
        EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, sizeof(gcm_tag), gcm_tag);
        /* Finalise: note get no output for GCM */
        rv = EVP_DecryptFinal_ex(ctx, outbuf, &outlen);
        /* Print out return value. If this is not successful authentication
         * failed and plaintext is not trustworthy.
         */
        printf("Tag Verify %s\n", rv > 0 ? "Successful!" : "Failed!");
        EVP_CIPHER_CTX_free(ctx);
 }

int main(int argc, char **argv)
{
        aes_gcm_encrypt();
        aes_gcm_decrypt();
 }

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